SQL 查询优化

Question

If I have a table that has 50 columns, will it take less time to use a statement like

SELECT id,name,description FROM table

or will it be the same as if I write

SELECT * FROM table

Answer 1

Always return the least number of columns possible to satisfy your needs.

Answer 2

If you don't need all the columns, it's certainly best to only select the ones you need. While it probably won't take MySQL more time to locate the rows, it will certainly be faster to send the results back to the client (since there is less data to return).

Answer 3

Selecting all columns always takes longer than selecting the columns you actually want. Try them out in PHPMyAdmin or something and have a look at the time they take to complete. For this, using a bigger table is a good idea to get times greater than 0.001 seconds and the like.

James